Fentanyl, N-(1-phenylethylpiperidin-4-yl)-N-phenylpropanamide, is a synthetic μ-opioid receptor agonist. Fentanyl in its free base form has the chemical structure:

Originally designed as an anesthetic, fentanyl has become an important tool for managing breakout pain in a clinical setting, with a potency roughly 100 times that of morphine (Peng and Sandler 1999). Fentanyl related compounds may produce stronger euphoric effects, which gives rise to a significant potential for misuse (Højsted and Sjøgren 2007; Sehgal and Smith 2012). Thus there is a need for chemical countermeasures (i.e., “antidotes”) to neutralize fentanyl related compounds' environmental and physiological threats.